The present invention relates to a method and a device for detecting a panic braking operation.
It is generally understood by xe2x80x9cpanic brakingxe2x80x9d that the driver of the vehicle actuates the brake pedal quickly and heavily. Systems for detecting a panic braking operation are known from the related art. Thus, German Published Patent Application No. 195 24 939, for example, describes a control system for a braking system in which in specific operating situations which are detected on the basis of the driver""s braking command, braking force exceeding the actual input from the driver is applied to the wheel brake. One of these operating situations is a situation in which a danger situation can be inferred from the driver""s response (panic braking). To detect this situation, the manner in which the driver actuates the brake actuating element is evaluated. If he/she actuates the element very quickly, which is detected, for example, on the basis of the change in the admission pressure of the braking system, pressure is built up beyond the driver""s input. If the evaluated quantity exceeds a predetermined threshold value (trigger threshold), then the automatic braking process, that is to say the increased braking force build-up takes place. In this context, the trigger threshold is changed on the basis of preselected performance quantities, the trigger threshold being lowered, that is the triggering of the increased braking force build-up is made more responsive when the danger potential increases. In this context, the admission pressure of the braking system, the vehicular speed, the vehicle""s rate of rotation, the transversal acceleration of the vehicle, the longitudinal acceleration of the vehicle, the steering-angle change, the engine power output and/or the brake-pressure request of a driving-dynamics controller are mentioned as performance quantities.
To detect a panic braking operation, such systems known from the related art need a relatively complex and thus expensive additional sensor technology such as brake pedal travel pickups, longitudinal acceleration sensors or yaw-rate sensors.
According to the present invention, a panic braking operation of a vehicle having at least two wheels is detected by
measuring speed quantities which represent the rotary motions of at least two wheels,
selecting the speed quantity of one of the wheels and/or by determining a speed value from the speed quantities,
determining a change value which represents the time-related change of the selected speed quantity and/or of the speed value,
determining the time characteristic of the change value,
detecting a panic braking operation as a function of the time characteristic of the change value.
The present invention has the advantage that no complex and expensive additional sensor technology is needed for detecting panic braking; the wheel-speed sensors which are provided anyway in anti-lock control systems, traction control systems, and/or vehicle stability control systems are sufficient. Thus, the use of a panic detection is also possible in so-called xe2x80x9clow-cost braking systemsxe2x80x9d.
Through the detection of a panic braking operation, it is possible to warn the following traffic in the event of a panic braking operation. Here, for example, one is thinking of activating the hazard warning system in response to a detected panic braking operation.
Moreover, provision can be made for the detection of a panic braking operation to be communicated via ranging systems (ACC systems, Automatic Cruise Control) so that vehicles that follow are heavily braked as well.
When detecting a panic braking operation, stability can be improved by carrying out a responsive initial control of the brake pressures at the wheels of the rear axle and/or of the front axle. In this manner, one avoids excessive wheel run-ins, accompanied by wheel instabilities.
Furthermore, provision can be made to limit the brake pressure at the rear wheels in response to a detected panic braking operation. This limitation can be maintained until an anti-lock control and/or a braking-force distribution control is activated at the rear wheels or a specifiable second period of time is exceeded or a specifiable minimum vehicle deceleration is undershot. Through this rate-of-change limitation of the pressure rise in the wheel brakes, an improvement of the braking distance is achieved since, with these elements, the excess brake pressure does not overly exceed the locking pressure level. Because of this, the following brake-pressure reduction can be kept small. Also, strong hydraulic throttling of the braking action at the wheel brakes of the rear axle, which results in an unsatisfactory brake pedal feel, can be reduced or eliminated.
In an advantageous refinement of the present invention, provision is made for the speed quantity of one of the wheels to be selected in such a manner that the speed quantity of the wheel having the lowest rotational speed is selected as the selected speed quantity. Thus, the slowest wheel is used as reference wheel. Alternatively or in addition to this, the speed value can be determined via a, possibly weighted, mean value generation from the speed quantities of at least two wheels.
Moreover, provision can be made for the speed quantities to be checked for errors, and for the speed quantities of the wheels at which an error has been detected to be excluded from the selection of the speed quantity and/or from the determination of the speed value.
It is also possible to detect whether the vehicle travels on a roadway having irregularities of a specifiable degree (rough-road detection). If such a rough road is present, the detection of the panic braking operation is deactivated.
Moreover, it is advantageous that only non driven wheels are used for selecting the selected speed quantity, that is the reference wheel, or for determining the speed value, respectively. In this manner, the influence of an engine drag torque, in particular on roadways having a low coefficient of friction, is ruled out.
The time characteristic of the change value as a function of which a panic braking operation is detected according to the present invention can be determined in such a manner that the change value, that is the negative wheel acceleration of the selected wheel, is compared to a first threshold value. A panic braking operation is detected if the change value further falls below a second threshold value within a specifiable first period of time subsequent to falling below the first threshold value. In this context, the first threshold value is greater than the second threshold value.
To make the detection of the panic braking operation more reliable, provision can be made for the actuation of the brake pedal to be detected via a braking signal. This can be done, for example, via the brake lights switch. In this embodiment, a panic braking operation is detected only if the braking signal indicates an actuation of the brake pedal.
Alternatively or in addition to this, provision can be made to determine a deceleration quantity which represents the deceleration of the whole vehicle. According to this embodiment, a panic braking operation is detected only if the deceleration quantity becomes greater over time.